The present invention relates generally to a process for producing a metal-coated paper and more particularly a metal-coated paper wherein the layer of metal material is applied to a paper backing material by a printing process.
Papers are known, which are printed with an ink material made up of metal powder and binding agent, using an intaglio printing process. If the endeavor is made to apply this process for producing such paper to the production of metal-coated packaging papers, it is found that there is a disadvantage that the metal coating on the composite paper material has only a limited resistance to abrasion. That problem becomes a matter of consequence in particular when such papers are to be processed on high-speed, electronically controlled automatic packaging machines. That is, unless the metal particles are very firmly bound into the coating, it is probable that metal particles will splinter off along the fold lines that are formed in the material when it is made into a package form, and the metal dust which is formed by the metal particles that come away in that manner can result in disturbances and defects in control of the automatic packaging machines.
In the past, metal-coated papers which were used in such automatic machines have been produced by a metal foil being applied to a paper carrier or backing material, in such a way as to form a lining thereon. Such composite materials wherein the metal foil comprises aluminum are extensively used in packaging cigarettes, with the metal foil paper composite material forming the lining of the cigarette box.
The fact that a cigarette pack is provided with a wrapping paper that is coated with aluminum represents a cost factor of some substance in that manufacturing operation. The costs involved include in particular the material costs which are incurred by virtue of the aluminum used and which depend on the amount of aluminium employed in making the composite material. If the aluminum foil is 7.mu. in thickness, the consumption of aluminium is about 20 grams per square meter of material. Depending on the stiffness of the outer enclosure used for the cigarette pack, which generally comprises cardboard, the thickness of the aluminum coating is between 6 and 15.mu.. The carrier material for the aluminum foil, to which the foil is therefore applied, is a thin, uncoated paper with a weight of about 22 to 40 grams per square meter.
In comparison with that, it would be very much less expensive to produce a paper provided with a metal coating comprising metal power and binding agent, by an intaglio printing process.